1. Field of the Invention
The present invention relates generally to the field of parametric loudspeakers used to produce useful audible sound. More particularly, the present invention is related to such loudspeakers that are provided in a very low profile, or thin, configuration.
2. Related Art
Non-linear transduction, such as a parametric array in air, results from the introduction of sufficiently intense, audio modulated ultrasonic signals into an air column. Self demodulation, or down-conversion, occurs along the air column resulting in the production of an audible acoustic signal. This process occurs because of the known physical principle that when two sufficiently intense sound waves with different frequencies are radiated simultaneously in the same medium, a modulated waveform including the sum and difference of the two frequencies is produced by the non-linear (parametric) interaction of the two sound waves. When the two original sound waves are ultrasonic waves and the difference between them is selected to be an audio frequency, an audible sound can be generated by the parametric interaction. Emitters suitable for producing such an effect are referred to herein as “parametric emitters.”
While parametric emitters have been produced using a variety of materials, including piezoelectric crystals, PVDF films, electrostatic emitters, other membrane-type acoustic transducers and the like, they have conventionally been constructed as rather large, bulky units or a larger array consisting of multiple transducers. However, current trends in visual displays are requiring ever slimmer televisions, computer monitors, point-of sale displays, and the like. Thus, while consumers can now obtain video components that have a very low profile (e.g., a very small thickness or depth), many times the speakers available for use with such video components have a much larger profile than the video component, somewhat negating the positive gains achieved in reducing the size of video displays. This is particularly true for parametric emitters, which have conventionally required relatively large cabinets to contain the required emittive material, circuitry, arrays, etc.
Even when a very thin emittive material is used in a parametric emitter (PVDF film, for example, is only a few thousandths of an inch thick), providing the required electrical circuitry, providing sufficient electrical coupling structure, and the like, has maintained the overly large profile of most parametric emitters. Also, reliable electrical coupling to very thin film, regardless of overall emitter thickness, has been a particular challenge with PVDF film.